The present invention relates to superparamagnetic image character recognition compositions and processes of making and using, and more particularly concerns image character recognition processes and printing processes and printed articles thereof.
In the process of electrophotographic printing, a photoconductive member is uniformly charged and exposed to a light image of an original document. Exposure of the photoconductive member records an electrostatic latent image corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed by bringing a developer material into contact therewith. This forms a powder image on the photoconductive member which is subsequently transferred to a receiver sheet and permanently affixed thereto in image configuration.
Electrophotographic printing has been particularly useful in the commercial banking industry by reproducing checks or financial documents with magnetic ink, that is by fusing magnetic toner particles thereon. Each financial document has characters or symbols imprinted thereon which are recognized as unique characters of a specified type font. The document, upon which the characters are printed, is advanced past a magnetizing station, or alternatively as referred to in the art, a "write" station, where the magnetizable ink is subjected to a magnetic field which magnetizes the ink in accordance with the unique geometry of the imprinted characters. The magnetic characters each have their own unique magnetic field which may be read by a magnetic ink character recognition (MICR) reader and processed.
The magnetic characters are susceptible to surface wear during magnetic writing and reading operations wherein the magnetic characters retain substantially all their visible printed image qualities but the "magnetic signature" or magnetic image properties of the characters can be substantially distorted, diminished, or altered. Additionally, the characters are highly susceptible to the aforementioned magnetic signature changes as a result of accidental or deliberate exposure of the magnetic characters to electromagnetic fields of a strength which is comparable to that the magnetic fields used to initially magnetize or magnetically "write" the printed characters in a MICR process. Thus, MICR processes and MICR printed products, as well as other articles which employ magnetically encoded characters, writings, or the like information, are susceptible to alteration by the influence of external magnetic fields or electromagnetic radiation.
The following United States patents are noted as being of interest to the background of the present invention.
U.S. Pat. No. 4,859,550 Patentee: Gruber et al. Issued: Aug. 22, 1989 PA1 U.S. Pat. No. 5,124,217 Patentee: Gruber et al. Issued: June 23, 1992 PA1 U.S. Pat. No. 5,140,368 Patentee: Szlucha Issued: Aug. 18, 1992 PA1 U.S. Pat. No. 5,219,554 Patentee: Groman et al. Issued: Jun. 15, 1993
Some relevant portions of the foregoing patents may be briefly summarized as follows:
U.S. Pat. No. 4,859,550, discloses an electrophotographic process which comprises the generation of latent image; developing the image with a toner composition comprised of resin particles, magnetite particles, and an additive component comprised of an aliphatic hydrocarbon or a polymeric alcohol of the formula CH.sub.3 (CH.sub.2).sub.n CH.sub.2 O H wherein n is a number of form about 30 to about 500; and subsequently providing the developed image with magnetic ink characters thereon to a reader/sorter device whereby toner offsetting and image smearing is minimized in said device.
U.S. Pat. No. 5,124,217, discloses an electrophotographic process for enabling substantially tamperproof images, including the generation of a latent image; developing the image with a toner composition comprised of resin particles, magnetite particles, and a colored organic soluble dye, a colored organic insoluble dye, or the salts thereof; and an optional additive component comprised of an aliphatic hydrocarbon or a polymeric alcohol of the formula CH.sub.3 (CH.sub.2).sub.n CH.sub.2 OH is wherein n is a number of form about 30 to about 500.
U.S. Pat. No. 5,140,368, a character printing and detection system in which a toner image is fixed to a sheet with each character of the toner image being inverted so that the normally leading edge of each character is the trailing edge. The toner image on the sheet is magnetized. The sheet of support material is reinverted so that the leading edge of each character of the toner image fixed to the sheet of the support material is the trailing edge. The intensity of the magnetic field generated by each character of the toner image fixed to the sheet is detected to identify each character.
U.S. Pat. No. 5,219,554, discloses hydrated biodegradable superparamagnetic metal oxides for use in biological imaging applications.
The disclosures of each of the aforementioned documents are totally incorporated herein by reference.
U.S. Pat. No. 5,358,659 (D/91332) assigned to the assignee of the present application, and which is incorporated herein by reference in its entirety, discloses a method of forming magnetic materials having tunable magnetic properties and the magnetic materials formed thereby. The magnetic materials contain both single-domain and multi-domain particles and have high initial permeability while maintaining coercivity and remanence in the material. A method for making a magnetic ferrofluid comprises providing a colloidal suspension of submicron ion exchange resin matrix, loading the resin matrix by ultrafiltration with a magnetic ion, precipitating single-domain particles within said resin and precipitating multidomain particles outside of the resin to form a stable colloidal dispersion of the resin and particles.
In the aforementioned commonly assigned U.S. Pat. No. 5,362,417 (D/90063) there is disclosed a method of forming a colloidal dispersion of submicron particles comprising: providing an ion exchange resin matrix; loading said resin matrix with an ion; and treating the resin to cause in-situ formation of submicron particles; and fluidizing said ion exchange resin and particles in an aqueous medium to form a stable colloid of the particles.
In commonly owned U.S. Pat. No. 5,321,770 there is disclosed a method for determining the boundaries of a symbol or word string within an image, including the steps of determining page orientation, isolating symbol strings from adjacent symbol strings, establishing a set of boundaries or references with respect to which measurements about, or further processing of, the symbol string may be made. Many of the references cited therein, including U.S. Pat. documents and other publications, provide exemplary methods for detecting, recognizing, and distinguishing characters and images by, for example, comparative means.
U.S. Pat. No. 4,474,866, assigned to the assignee of the present application, discloses a developer composition containing superparamagnetic polymers. The developer composition disclosed in this patent consists of a dispersion of fine particles of iron oxide in a polystyrene ion exchange resin. More specifically, the developer composition consists of .gamma.-Fe.sub.2 O.sub.3 (gamma) disposed in a sulfonated divinylbenzene cross-linked polystyrene resin.
The disclosures of each of the aforementioned commonly assigned documents are totally incorporated herein by reference.
The present invention also relates to processes for preparing magnetic marking compositions having substantially only rotationally free, single domain magnetic particles. More particularly, the present invention relates to magnetic marking compositions possessing novel magnetic properties including: being free of barriers to a change in system magnetization (M); having substantially no magnetic memory or hysteresis; having high initial magnetic permeability; the magnetic response of the composition becomes infinite up to about the saturation magnetization of the composition upon application of a magnetic field (H); temperature and magnetic field dependent magnetic properties; solid-liquid phase dependent reversible superparamagnetic to paramagnetic properties; low magnetic resistivity; electrically insulating; and exceptionally high resistance to quantum tunneling above about 0.degree. K.
The present invention also relates to methods for forming and manipulating the magnetic properties of isolated nanocompass particles, for example, the size or dimensions of the single domain may be controlled to a great extent by the strength and duration of an externally applied pulsed electromagnetic field that is used to "carve" or etch individual domains, interstices or cavities within a continuous solid or gel phase during the preparation of the superparamagnetic marking compositions.
The term "domain" as used herein is described, for example, in C. P. Bean and J. D. Livingston, J. AppL Physics, 30, 120 (1959); and B. D. Cullity, Introduction to Magnetic Materials, Addison-Wesley Publishing Co., Mass., (1972), which are incorporated by reference in their entirety, and refers in the case of single domain particles of the present invention to, for example, discrete magnetically isolated and non interacting superparamagnetic nanoparticles. Although not wanting to be limited by theory, it is believed that the presence of substantially or exclusively single-domain crystallites in the compositions of the present invention enable the aforementioned combination of novel magnetic properties and applications thereof.
Properties of magnetic fluids are disclosed, for example, in Magnetic Fluids Guidebook: Properties and Applications, V. E. Fertman, Hemisphere Publishing Corp., N.Y., 1990, the disclosure of which is incorporated herein by reference in its entirety. The magnetic properties of magnetic fluids as a function of temperature have been extensively studied. For example, for conventional ferromagnetic or ferrimagnetic single-domain particles, spontaneous magnetization disappears at a certain temperature known as the Curie point(T.sub.c), also known as the magnetic transition temperature. At the Curie point, the exchange atom interaction energy is equal to the thermal interaction energy, and the substance becomes paramagnetic. The upper Curie point is the temperature above which ferroelectric materials lose their polarization and the lower Curie point is the temperature below which some ferroelectric materials lose their polarization. When ferromagnetic materials become paramagnetic at the Curie point the material exhibits the so-called Curie-Weiss effect or behavior.
There exists a need for image character recognition systems, imaging processes, compositions, articles, and devices, that are suitable for use in MICR like applications with the exception that the images and articles containing magnetically encoded information formed thereby are resistant to distortion, and immune from distruction, under the influence of external magnetic fields.
There remains a need for magnetically recognizable marking materials which are not destroyed or altered under the influence of a external electromagnetic fields and which materials can be used in a wide variety of printing processes and printing devices, such as dry and liquid xerographic printing, ionographic printing, lithographic printing, grauvre printing, thermal ink jet printing, impact printing, and applications. There also remains a need for magnetically recognizable marking materials which are single domain and rotationally free at temperatures of about 10.degree. K. and above.
Still further, there is a need for magnetically recognizable marking materials that permit economical, clean, and optionally dry micron and submicron polymeric composite particles that can be selected for use in a magnetic liquid or solid marking formulations, and utilized as an active component in superparamagnetic marking fluids, gels and solids, and in printing and character recognition processes.
Solutions to the above problems and needs have been unexpectedly found in the compositions and processes of the present invention wherein there is provided superior superparamagnetic marking materials that enable, for example, novel image character recognition processes and printed matter, wherein the individual magnetic moments contained in the nanomagnetic crystalline species contained in the marking material are freely rotating, single domain, and therefore easily and independently oriented in low, intermediate, and high magnetic fields.
In embodiments of the present invention, solutions to the aforementioned problem are provided.